Minor but necessary improvements to WAL keepalives

Fujii Masao

src/backend/replication/walreceiver.c

@@ -750,7 +750,8 @@ ProcessWalSndrMessage(XLogRecPtr walEnd, TimestampTz sendTime)
 	walrcv->lastMsgReceiptTime = lastMsgReceiptTime;
 	SpinLockRelease(&walrcv->mutex);
 
-	elog(DEBUG2, "sendtime %s receipttime %s replication apply delay %d transfer latency %d",
+	if (log_min_mesages <= DEBUG2)
+		elog(DEBUG2, "sendtime %s receipttime %s replication apply delay %d ms transfer latency %d ms",
 					timestamptz_to_str(sendTime),
 					timestamptz_to_str(lastMsgReceiptTime),
 					GetReplicationApplyDelay(),

src/backend/replication/walsender.c

@@ -834,7 +834,12 @@ WalSndLoop(void)
 			if (pq_is_send_pending())
 				wakeEvents |= WL_SOCKET_WRITEABLE;
 			else
+			{
 				WalSndKeepalive(output_message);
+				/* Try to flush pending output to the client */
+				if (pq_flush_if_writable() != 0)
+					break;
+			}
 
 			/* Determine time until replication timeout */
 			if (replication_timeout > 0)